Stirring devices are already known which, by means of torque measurements, make it possible to obtain information concerning the change in viscosity of the medium that is to be stirred (cf. Holland and Chapmam: Liquid Mixing and Processing in Stirred Tanks, Reinhold Publishing Corporation, New York, pp. 42-49, 1966). In this regard, for the measurement of the torque there is often provided a torsion measurement shaft which is arranged between the drive shaft of the stirring mechanism and the stirring tool. The torque that is introduced into the medium that is to be stirred then causes a defined twisting of the measurement shaft, which is detected by means of suitable sensor technology.
In this regard, it is particularly disadvantageous that the torsion measurement shaft is connected with the stirring mechanism drive in a fixed fashion, which results in a correspondingly long design of the stirring device, that, in practice, gets in the way most of the time. Since torsion measurement shafts can be loaded with only very slight bending stresses, a correspondingly unwieldy and statically overdefined arrangement of bearings is necessary, which can lead to measurement inaccuracies. In addition, the complex, multiple arrangement of bearings and the difficult measurement of the bending deformation on the turning measurement shaft are linked with a not insignificant cost burden. Furthermore, the torsion measurement shaft can be placed only under a limited torque loading, for which reason the previously known stirring devices are used almost exclusively for measurement purposes.
From CH-PS 641 973, a stirring apparatus is also already known, whose stirring mechanism has a separate housing with two separable housing parts that can be fastened to one another, in conjunction with which the one housing part is provided on the stirring drive and the other on the stirring shaft. To connect the housing parts, the drive shaft of the stirring mechanism has in addition a shaft coupling which in its functional position engages with a mating coupling on the stirring shaft. Between the two housing parts there can be placed an intermediate housing, which has two intermediate housing parts, which can turn in opposite directions by means of a pivot bearing, and one of which is joined to the housing part that is provided on the stirring drive, while the other is joined to the housing part of the stirring mechanism that accommodates the stirring shaft.
In addition, there is provided in the intermediate housing an intermediate shaft, which is placed in an in-line arrangement between the driven shaft and the stirring mechanism shaft, and which is supported in a rotatable fashion in both of the intermediate housing parts. The two housing parts of the stirring mechanism can thus rotates in opposite directions by means of the pivot bearing in the intermediate housing, so that following the fixing of the housing part that is joined with the stirring shaft to a torque support that is joined to the stirring drive in such a way that it cannot turn, the reaction force of the torque that is being introduced into the medium that is to be stirred can be measured.
A disadvantage of this previously known apparatus consists primarily in the fact that it requires a specialized stirring mechanism with a two-piece housing. In the case of stirring mechanisms with a one-piece housing or with a stirring shaft that is uninterrupted and passes all the way through, the intermediate housing is practically unusable. Also unfavorable in addition is the fact that the numerous pivot bearings require a certain expense, and decrease the mechanical stability of the stirring mechanism as well. A further disadvantage consists in the fact that the intermediate housing increases the overall length of the stirring mechanism, which makes it more difficult to handle.